IMI Hi-Torque Starter Setup Part II

I checked the actual engagement of the pinion in the flywheel per IMI’s request. After taking a few measurements I was able to determine that I had roughly 60% engagement at best. [(Flywheel teeth width 0.444″) – (Distance of engaged pinion and edge of flywheel teeth 0.084″) – (Pinion tooth taper 0.078″)] = 0.282″ Engagement. Or [(0.444″ / 0.282″)x100] = 63.5% engagement. Matt at IMI and I agreed that this was not enough engagement. Matt told me that they have a Pontiac test block where they check every 25th unit as a quality measure. The test block utilizes an automatic flex plate instead of a flywheel. Matt also said that there is a local Pontiac club where a fair number of members have installed the IMI starter without issue. We then discussed backlash. When the starter was bolted to the block without any shims, backlash measured in at 0.044″. This was verified by sticking a piece of welding wire between the teeth. I started with the smallest diameter. The idea is to keep stepping up to a larger diameter until ideally one no longer fits. In my case .044″ was the largest available at the time. The fit of the 0.044″ welding wire was slightly snug so actual backlash is not far from that value. IMI specs appropriate backlash between .020″ and .030″. The starter was shipped back to IMI in Whittier CA on Tuesday December 8th to be machined to fit my application.

8 Responses to “IMI Hi-Torque Starter Setup Part II”

I read your story about the IMI starter and the problem you had. I was in the same boat with mine. Called IMI direct and they sent me a direct replacement with the aluminum block machined so starter gear engages now 100%.
Now I have another problem and that’s why I wrote. Your ninth pictures above shows the starter gear engaged in to the flywheel/flex plate with a small gap between the ring that is mounted in front of the starter gear drive and the teeth of the flywheel/flex plate. I would say about a 1/16 of an inch. by looking at that picture. That same ring on my starter is about as close to the flywheel that only a hair would fit in between.
Do you have any recommendations on how to fix my problem? I could put more shims under the aluminum block to lower the starter to increase the distance between the ring and flywheel, but I use already four shims. Is there a max. on shims I can use?

I definitely see your concern. You don’t have any side to side adjustment so as you mention the only option to gain some clearance here would be to shim the starter down. My first thought would be to make sure the backlash is correct before you make any more adjustments. Backlash will determine the limitation on the number of shims you can use. Were you able to get a backlash measurement? You should be somewhere around 0.020″ to 0.030″. Also, make sure you have adequate engagement into the flywheel. I did not. There’s more pictures on the third write up that you may have not seen yet. These pictures show the corrected engagement after I received the modified part back from the manufacturer.

IMI sent me a brand new replacement starter after I explained the engagement issue with the new one having 0.06 inches taking off at the casing. They knew about the problem and are actually good folks to deal with. Mine engaged about 40-50% no shim installed. Now I have 100% engagement.
I am on the lower part of back lash around 0.020. So as you mentioned I may get away by using another shim to gain some clearance between the ring on the starter drive and the flywheel teeth.
The car is a 77 TA with a 70 455HO 4 speed. It is a work in progress. It started with a full rotisserie resto.

Nice choice on the 77 TA. Sounds like you may be ok with an extra shim as long as you’re still in the backlash tolerance band afterward. May be a good idea to check a few locations around the flywheel to make sure you still have clearance. My starter has been going strong for several years now with no complaints. I think you’ll be very pleased with it once you get all the gremlins worked out. Next project on mine will probably be swapping pulleys and installing an updated steering gear. Keep us updated on how your starter install turns out!

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